In recent years, with the development of high-properties and networking of computer and information communication equipment, to reach high-speed transmission and deal with large-capacity information, operation signals tend to be high-frequency. Therefore, the material of the circuit substrate material is required to improve.
Among the conventional materials used for the printed circuit substrate, the epoxy resin with excellent adhesion characteristics is widely used. However, the epoxy resin circuit substrate has relatively high dielectric constant and dielectric loss tangent (dielectric constant is more than 4, dielectric loss tangent is around 0.02), and inadequate high-frequency characteristics, which results in failure in meeting the requirement of high-frequency signals. Therefore, it is require to use resins with excellent dielectric properties. That's, the resin has low dielectric constant and dielectric loss tangent. For a long time, technicians in the field have studied thermosetting polybutadiene or butadiene copolymer resin with excellent dielectric properties. The results of these studies are cited as follows:
U.S. Pat. No. 6,569,943 disclosed to use amine modifer polybutadiene liquid resin with vinyl added with monomers of low molecular weight as curing agent and diluent, and use impregnates fiberglass cloth to make circuit substrate. Although the dielectric properties are excellent, the resin system is liquid at normal temperature, and so can not be made into tack-free prepreg. Therefore, in the compression moulding of sheet, it is difficult to adopt common stacked technology of prepreg, which results in difficult process operation.
U.S. Pat. No. 5,571,609 disclosed to use 1,2-polybutadiene resin or polyisoprene with molecular weight less than 5,000, and nonpolar butadiene styrene copolymer with high molecular weight, added with many silica as filler, and use fiberglass cloth as reinforcing material to make circuit substrate. Although it has excellent dielectric properties, the processing property of the process of making the prepreg gets bad, because contents of high molecular weight are adopted to solve the tacky problem of prepreg in this patent. Furthermore, since the proportion of the rigid benzene ring in the resin molecules of the whole resin system is very low, and since the cross-linked chain segments mostly are composed of methylenes with low rigidity, the made substrate has bad rigidity, and the bending strength is very low.